There is a demand for a propulsion unit to be used underwater by swimmers, specifically those snorkeling or scuba diving. The term "swimmer" used herein includes surface swimmers, and underwater swimmers, often referred to as divers. Propulsion units are also used by lifeguards, and certain handicapped or disabled people. There is also a need for such units by the military. Some of these devices include sleds which are power operated, other include back packs wherein a propulsion unit is attached to the back of a swimmer. A typical example of a sled is shown in U.S. Pat. No. 4,813,367 to Stevenson. Examples of propulsion devices for mounting on the back of a swimmer are shown in U.S. Pat. No. 3,916,814 to Bardoni et al, in U.S. Pat. No. 3,995,578 to McCullough, and in U.S. Pat. No. 4,467,742 to Duboy.
Most motorized sleds are fairly large units and require a swimmer to mount the sled and drive it as a separate vehicle. The back powered units are sufficiently compact that they remain with the swimmer. In some cases, however, the back powered units extend for some distance out from the divers air bottle and thus are bulky. The units are awkward for a diver to enter and leave the water. Furthermore, these units are not easy for a swimmer to maneuver in the water because the propulsion unit is always fixed to the swimmer.